1. FIELD OF THE INVENTION
This invention relates to a method and system for multiplexing a signal for transmission. More particularly, this invention relates to a method and system of the kind above described which can be applied to a transmission means incapable of transmitting d.c. components such as a recording and reproducing system using a magnetic recording medium so that a signal including such d.c. components can be transmitted and which are also suitable for transmission of a plurality of information.
2. DESCRIPTION OF THE PRIOR ART
One of known methods for transmitting a signal comprises subjecting a pulse signal to pulse position modulation, pulse interval modulation, pulse width modulation, pulse amplitude modulation or the like by the signal to be transmitted. Further, it is known that a pulse signal consisting of pulses of positive and negative polarities is advantageously used as a carrier signal when it is desired to transmit a signal with high fidelity by use of a transmission medium incapable of transmitting d.c. components such as one used in a magnetic recording and reproducing system or by use of a transmission medium in which a signal transmitted is susceptible to amplitude variations.
A method of transmission utilizing a pulse signal as a carrier as above described can be effectively used when a wide-band video signal is converted into a narrow-band signal for the transmission of the video signal by a narrow-band magnetic recording and reproducing system or by a transmission means adapted for the transmission of an audio signal. In the case of transmission of such narrow-band signal, the period of time required for the transmission is very long compared with that required for the original signal due to the fact that a pulse signal having a low pulse recurrence rate is generally employed as the carrier. When a signal to be transmitted is a television signal which consists of a video information signal, a horizontal synchronizing signal and a vertical synchronizing signal, transmission of this television signal by directly converting same into a narrow-band pulse signal results in the existence of a dead transmission time. More precisely, the synchronizing signals in the television signal are also extended in respect of time, and the period of time occupied by these synchronizing signals relative to the actually required video information provides a dead time.